Prior apparatii and methods have been used for drilling underground arcuate paths under and around obstacles. Such techniques use a directional drill or jet attached to a drill string. The directional drill or jet is used to drill a path from one side of the obstacle, going under and/or around the obstacle and exiting on the opposite side of the obstacle. A reamer can be attached to the drill string or washover pipe and pulled back through the hole to further enlarge the diameter of the hole. Reamers of consecutively larger diameters can be pushed and pulled back through the hole until a desired diameter is reached. The reamer is then attached by a swivel connected to the casing intended to be installed in the hole. The reamer is then pulled back through the hole followed by the swivel connection to the casing until the casing occupies the hole. A swivel is required to keep torque from being transmitted from the drill string and reamer to the casing.
Drilling fluid or mud is used to power the jetting action of the reamer and to clean the drilled hole of cuttings. Five to fifteen barrels per minute of mud must be pumped to power a typical reamer. A job lasting several days can require thousands of barrels of mud to complete the reaming operation.
Since the hole is open at both ends during the reaming operation, mud exiting the reamer will follow the path of least resistance. The operator has little or no control over which end of the hole the mud will exit. In all prior methods the mud was supplied to the reamer from the rig side of the hole, exited at the reamer and then flowed out of the hole. Mud exiting on the side opposite the rig side of the hole required transport back to the rig side of the hole or disposal.
Disposing of the drilling mud often requires that the mud be hauled off to a disposal site. Hauling costs of $2.00 to $3.00 per barrel are typical and special sites are often required due to regulations and environmental issues. Transporting the mud back to the rig side is also costly since the obstacle being traversed is often a waterway and the closest bridge over such waterway could be, for example, 35 miles up or down the waterway.
Prior swivels did not have the capability of allowing fluids to pass therethrough while subjected to large tensions. Additionally, such swivels did not totally protect the piston from stresses being placed upon the swivel. In the event of failure the entire piston would need to be replaced. Improvements are also needed to reduce periodic maintenance required to replace the grease or other hydraulic medium which has escaped from the swivel.
A need therefore exists for apparatii and methods for recirculating mud when drilling underground arcuate paths.